1. Field of the Invention
The present invention relates generally to nozzles. More specifically, it relates to a nozzle having an undulating exit lip and/or a primary flow passageway defined by a cross-section that undulates about its periphery, which enhances mixing of a primary flow of a fluid (including a gas, liquid, or gas/liquid mixture) with a secondary flow of the first or a second fluid, or with ambient air, to achieve noise suppression and/or thrust augmentation without requiring the use of an ejector.
2. Description of the Related Art
Effective mixing of fluids from a nozzle with other fluids or ambient air is useful to a number of fields. Fluids, by this definition, broadly covers gases, liquids, and gas/liquid mixtures and any particulates they may carry, A flow, then, is a moving fluid. Nozzles which effectively enhance the mixing of so-called primary flows with secondary flows or ambient air are successfully employed in, and are useful to, the following applications: (i) jet engine nozzles; (ii) industrial spraying; (iii) public waste management systems; (iv) automotive fuel delivery systems; and (v) industrial mining. The exact configuration of an effective mixing nozzle will likely be application specific, dependent on the underlying purpose for the mixing.
A primary consideration in jet engine nozzle design is noise suppression. Noise suppression has traditionally been accomplished by mixing the primary flow of air from the engine with either a secondary flow of slower moving air or with the surrounding air in order to reduce the overall speed of the flow from the engine. Ejectors are devices which create and channel the secondary flow of slower moving air which then is mixed with the primary flow. As such, they have proven useful as means for noise suppression. This noise suppression occurs as the secondary flow from the ejector mixes and slows down the primary flow. Unfortunately, the effective thrust is diminished in the process. In addition, the use of an ejector adds to the cost, complexity and weight penalty of the jet engine. Overall, noise suppression through ejector technology is a trade-off with performance. Better noise suppression comes at a cost of lower performance, and vice versa. In a field where small differences in performance and cost matter greatly, the necessary presence of an ejector is significant.
Successful design of nozzle systems for supersonic commercial aircraft involves meeting both environmental and economic metrics. For nozzles, the environmental metric is noise, as expressed in the FAR 36 Stage III regulations. Economic metrics are usually associated with both take-off and cruise aeroperformance, weight, mechanical complexity, and structural reliability. As such, a successful nozzle design would be one that concurrently maximizes noise suppression and minimizes the loss of aeroperformance or, preferably, even improves aeroperformance. To date, no nozzle technology has been able to offer both improved aeroperformance (i.e. thrust augmentation) and noise suppression.
Current methods of designing nozzles for supersonic commercial applications rely heavily on state-of-the-art empirical methods. This is accomplished through the use of massive data sets from prior nozzle testing. This process is cumbersome and expensive. (See Seiner, J. M., and E. A. Kresja, 1989, Supersonic Jet Noise and the High Speed Civil Transport, AIAA Paper 89-2358, AIAA/ASME/SAE:/ASEE 25 Joint Propulsion conference, Jul. 10-12, 1989/ Monterey, Calif.) The most successful nozzle designs are based on nozzle geometry that controls the strength of shock waves, that can rapidly mix high and low speed flow streams effectively, and produce noise spectrally outside the range of Noy weighting. Present nozzle designs that are effective at reducing noise at low jet exhaust velocities must make a disappointing trade off with nozzle performance. This is especially true in the case of subsonic jet noise reduction where noise reduction is achieved primarily through an increase of engine by-pass ratio which leads to low mixed flow velocities.
Some attempts have been made to optimize both the aeroacoustic suppression characteristics and suppressed mode performance in nozzle design, especially for those targeted towards operation at low jet exhaust velocities. On the lobed mixer of Presz, counter-rotating axial vorticity generated by mixer lobes is used to mix high speed engine primary core and fan stream flow with entrained lower speed secondary flow from an ejector inlet. (See Presz, Jr., Walter M. 1991, Mixer/Ejector Noise Suppressors, AIAA Paper 91-2243, 27th Joint Propulsion Conference, Jun. 24-26, 1991/ Sacramento, Calif.) The enhanced mixing is used to both increase the level of secondary flow entrainment and mix high and low stream flow to achieve lower speed uniform ejector exit velocity that has an acceptable level of external jet noise. An ejector, with its attendant deficiencies, is required to take advantage of counter-rotating vorticity created by the mixer lobe geometry. The current state-of-the-art technology has not yet adequately related the design of lobe geometry to prediction of circulation strength of counter-rotating vorticity nor has it determined the circulation strength required to achieve full mixing in the shortest possible ejector duct. Additionally, both aeroperformance computations and nozzle internal noise computations cannot be treated with sufficient accuracy to optimize the design. A similar observation of nozzle suppression effectiveness has been made for other nozzle concepts.
Others advocate a different approach to nozzle noise suppression. Some propose mounting devices inside the nozzle flow passageway (e.g. fingers) or at the nozzle exit (tabs) in order to destroy the usual plume structure, create additional mixing layers and reduce jet velocity thereby favoring noise suppression. (See Ahuja, K. K., 1993, Mixing Enhancement and Jet Noise Reduction Through Tabs Plus Ejectors, AIAA Paper 93-4347, 15th AIAA Aeroacoustics Conference, Oct. 25-27, 1993/ Long Beach, Calif., Also See Krothapalli, A. and King, C. J., 1993, The Role of Streamwise Vortices on Sound Generation of a Supersonic Jet, 15th Aeroacoustics Conference, Oct. 25-27, 1993/ Long Beach, Calif.) These devices, however, are sources of additional drag, resulting in significant aeroperformance penalties. Mechanical devices, like fingers, add to the cost and complexity of the nozzle and often require a secondary flow from an ejector. Tabs, which protrude into the primary flow, show promise in disrupting and mixing the flow. While offering some noise suppression benefits, tabs do not offer any advantage augmenting thrust. Others have suggested "notching" or "slotting" nozzle ends to improve mixing. Like tabs, slots may improve mixing somewhat but they too do not offer any advantage in augmenting thrust. The same penalties are seen in the "transition nozzles" application analyzed by Sobota, in which the nozzle passageway is altered, for example, from a round cross-section to a rectangular cross-section at the exit in order to separate the flow and create counter-rotating vorticity. (See Sobota, Thomas, 1992, Final Report: Reduction of Supersonic Plume Noise through the Controlled Introduction of Axial Vorticity, NASA--Langley Research Center, SBIR Program, Contract #NAS1-19514, Oct. 1, 1992/Highttown, N.J.) Swept steps and centerbodies are used in conjunction with the nozzle shape `transition` to further separate the flow. Even though counter-rotating vorticity is introduced into the flow, the resultant location and strength of the counter-rotating vorticity minimize any advantage obtained.
There is an ever present need for new, improved nozzle designs for enhancing the mixing of a primary flow with a secondary flow or ambient air to achieve noise suppression and/or thrust augmentation for a jet engine nozzle without requiring the use of an ejector. In addition, there is a need for such nozzles which allow for ready optimization without involving the cumbersome and expensive process of designing and altering jet nozzles from the empirical analysis of massive data sets (a trial and error method).
Nozzles utilizing lobed mixers with an ejector or nozzles with one or more slots, fingers, or tabs suffer from the disadvantages of requiring an ejector, requiring a substantial trade-off between noise-suppression and aeroperformance, having no allowance for simultaneous noise suppression and thrust augmentation, and/or having the incapability of optimization through geometric nozzle parameter variation control.